CN109788938B

CN109788938B - Micromechanical control system for a piezoelectric transducer

Info

Publication number: CN109788938B
Application number: CN201780060828.8A
Authority: CN
Inventors: C.皮特斯; T.罗兹尼克; J.斯特勒; A.杜尔
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2016-09-30
Filing date: 2017-09-14
Publication date: 2022-02-18
Anticipated expiration: 2037-09-14
Also published as: US10856837B2; CN109788938A; US20180092623A1; DE112017004438T5; WO2018059959A1

Abstract

A system for detecting blood flow velocity within a vessel includes a transducer array including a plurality of transducers. Each of the transducers comprises: a carrier substrate; at least one spacer extending upwardly from the base; a transducer element attached to the spacer such that the piezoelectric transducer is spaced apart from the substrate; and a set electrode positioned on the upper surface of the substrate below the piezoelectric transducer. The tilt control system is configured to apply a bias voltage to the set electrode that causes the transducer element to pivot about a pivot axis between a first tilt position and a second tilt position.

Description

Micromechanical control system for a piezoelectric transducer

Technical Field

The present disclosure relates generally to systems and methods for measuring blood flow velocity, and in particular to systems and methods for measuring blood flow velocity using a phased array.

Background

Currently, there are no non-invasive small wearable sensors that are capable of detecting blood pressure of a human test subject. Non-invasive blood assessment (estimation) has many medical and personal benefits. In many cases, detecting a person's stress level can prevent a heart attack or avoid burnout if blood pressure is monitored over a longer period of time. Therefore, there is a need for a sensor capable of estimating blood pressure that enables monitoring of blood pressure over a longer period of time.

One of the main challenges of the measurement principle described in this section would be to find the exact position of the artery with respect to the transducer array with a very high angular resolution. For blood flow velocity measurements, it is necessary to know this angle accurately so the artery can be scanned correctly for optimal signal quality (SNR) and to minimize power in the wearable device. Therefore, a new concept that enables the detection of the location of an artery with high spatial and angular resolution will be proposed in the present patent application.

Drawings

Fig. 1 depicts an ultrasonic piezoelectric transducer 10 according to one embodiment of the present disclosure.

Fig. 2 depicts an embodiment of a system 30 for detecting blood flow velocity and measuring blood pressure using the piezoelectric transducer 10 of fig. 1.

Fig. 3 depicts an alternative embodiment of a piezoelectric transducer for use with the system of fig. 2.

Fig. 4 depicts another alternative embodiment of a piezoelectric transducer for use with the system of fig. 2.

Fig. 5 depicts a 1 x N array of transducer elements for a phased transducer array.

Fig. 6 depicts an N x 1 array of transducer elements for a phased transducer array.

Fig. 7 depicts an array of M x N transducer elements for a phased transducer array.

Fig. 8 is a schematic depiction of a phased transducer array with beam steering (beam steering) along the X-axis of the array.

Fig. 9 is a schematic depiction of a phased transducer array with beam steering along the Y-axis of the array.

Fig. 10 is a schematic depiction of a phased transducer array depicting the measurement angles of the transducers.

Fig. 11 depicts an embodiment of a transducer element for a phased transducer array.

Fig. 12 schematically depicts a phased array transducer misaligned relative to a blood vessel.

Fig. 13 schematically depicts a side view of the phased array transducer of fig. 12.

Fig. 14 is a top view of a piezoelectric transducer with a micromechanical adjustment member.

Fig. 15 is an elevation view of a first side of the transducer of fig. 14.

Fig. 16 is an elevation view of a second side of the transducer of fig. 14.

Fig. 17 shows the piezoelectric transducer of fig. 14 in a first tilted position.

Fig. 18 shows the piezoelectric transducer of fig. 14 in a second tilted position.

Fig. 19 is a block diagram of a combined multiple-input multiple-output (MIMO) array and phased array blood flow velocity detection system.

Fig. 20 is a schematic diagram of a dual station (bistatic) version of the combined multiple-input multiple-output (MIMO) array and phased array blood flow velocity detection system of fig. 19.

Detailed Description

For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. It will be further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one of ordinary skill in the art to which the disclosure relates.

An ultrasonic piezoelectric transducer 10 according to one embodiment of the present disclosure is depicted in fig. 1. The ultrasonic piezoelectric transducer 10 includes a piezoelectric substrate 12, an upper electrode 14, and a lower electrode 16. The piezoelectric substrate 12 is formed of any suitable piezoelectric material, including, for example, lead zirconate titanate or aluminum nitride. If the manufacture of the sensor device involves a CMOS process, aluminium nitride may advantageously be used, since aluminium nitride is compatible with CMOS processes.

The upper electrode 14 and the lower electrode 16 are formed of a conductive metal, such as aluminum, an aluminum alloy, platinum, tantalum, or any other suitable conductive metal. As schematically depicted in fig. 1, the upper electrode 14 and the lower electrode 16 are configured to be electrically connected to a signal control system 18 that includes signal generating and/or receiving components.

The piezoelectric transducer 10 is supported on a carrier substrate 20. The carrier substrate 20 serves as a carrier for the piezoelectric transducer 10 and also as a coupling member for coupling the signal generated by the piezoelectric transducer 10 to the underlying skin and tissue. The substrate 20 includes a lower surface 22 and an upper surface 24. The lower surface 22 of the base 20 is configured to be placed against a flat surface 26, such as a flat skin area on a patient's body. The upper surface 24 is located on the opposite side of the substrate from the lower surface 22 and is a generally planar surface to which the piezoelectric transducer 10 is attached.

The upper surface 24 is configured to orient the piezoelectric transducer 10 at a fixed non-zero angle relative to the planar surface 26. To this end, the substrate 20 is manufactured in a manner that causes the upper surface 24 of the substrate 20 to be inclined at a predetermined angle α with respect to the lower surface 22 of the substrate 20. The predetermined angle alpha corresponds to a desired angle of incidence of the ultrasonic signal or wave emitted by the transducer.

The angle of incidence is the angle between a plane defined by the lower surface 22 of the substrate 20 or by the planar surface 26 and a line L perpendicular to and intersecting the planar surface of the transducer 10. The upper surface 24 of the substrate is configured to orient the piezoelectric transducer at a predetermined angle of incidence α, which is greater than 0 ° and less than 90 °. The predetermined angle of incidence α enables a single piezoelectric transducer 10 to be used to determine blood flow velocity based on the doppler effect (explained in more detail below).

In addition to supporting the transducer 10 at a fixed angle of incidence α with respect to the planar surface 26, the substrate 20 is also configured to serve as a coupling member for coupling ultrasound signals between the piezoelectric transducer 10 and the underlying skin upon which the substrate is placed. Preferably, the substrate 20 is formed of talc ceramic (steatite ceramic) because talc ceramic creates a dry transition to the skin. Alternatively, any suitable substrate material may be used.

Fig. 2 depicts an embodiment of a system 30 for detecting blood flow velocity and measuring blood pressure using the piezoelectric transducer 10 of fig. 1. The system 30 is a two-station system comprising a single ultrasonic piezoelectric transmitter 10a and a single ultrasonic piezoelectric receiver 10 b. The transmitter 10a and the receiver 10b each have the same angle of incidence α and are arranged mirror-symmetrically with respect to each other. In one embodiment, the transmitter 10a and receiver 10b are incorporated into a housing 28 that holds the transmitter 10a and receiver 10b in a fixed position relative to each other. The housing 28 may be configured as a handheld device housing and/or may be incorporated into a wearable article that may be worn on a portion of a user's body, such as the user's arm, leg, or chest.

The system 30 includes a signal generator 32 electrically connected to the piezoelectric transmitter 10 a. The signal generator 32 is configured to actuate the piezoelectric transmitter 10a to generate the desired ultrasonic signal 38. To determine blood flow velocity using the doppler effect, the signal generator 32 is configured to actuate the piezoelectric transmitter 10a to emit an ultrasound signal at a predetermined frequency in a pulsed or continuous wave manner. In one embodiment, the predetermined frequency is in the range of 2 MHz to 10 MHz. In one particular embodiment, the predetermined frequency is approximately 4 MHz.

The ultrasound signal is directed towards the blood vessel 36 and reflected by the blood vessel 36 at an angle that depends on the angle of incidence α of the transducer 10 a. The piezoelectric receiver 10b receives the reflected ultrasonic signal 40 and converts the signal into a corresponding electrical signal. The signal processor 34 is electrically connected to the piezoelectric receiver 10b and is configured to process the electrical signals to determine the blood flow velocity in the blood vessel.

In one embodiment, the signal processor 34 is configured to evaluate the electrical signals from the piezoelectric receiver 10b to determine radial blood flow velocity based on the doppler effect. For example, the received signal 40 has a doppler shift due to the movement of blood cells. The signal processor is configured to determine a doppler shift of the received signal and calculate a radial blood flow velocity from the doppler shift. The signal processor may be configured to determine the radial blood flow velocity from the doppler shift in any suitable manner known in the art.

The signal processor may also be configured to determine a blood pressure value within the blood vessel. As is known in the art, there is a direct relationship between blood flow velocity in a blood vessel and blood pressure. Thus, once the blood flow velocity is determined, an estimate of blood pressure can be determined. The signal processor may be configured to determine the blood pressure value from the blood flow velocity in any suitable manner.

To actuate the

piezoelectric transducers

10a, 10b and process the received signals, the signal generating and processing devices 32, 34 may include a processor (not shown), such as a central processing unit, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) device, or a microcontroller. The processor may be configured to execute programmed instructions stored in a memory (not shown).

Referring now to fig. 3, an alternative embodiment of a piezoelectric transducer 10' is depicted that may be used with the blood flow velocity detection and blood pressure measurement system 30 of fig. 2. The piezoelectric transducer 10' of fig. 3 is a distributed piezoelectric transducer. The distributed piezoelectric transducer 10' is formed by dividing the piezoelectric transducer 10 of fig. 1 into a plurality of individual smaller transducers 42 along one dimension. Multiple transducers 42 are connected together in a line and operate as a single piezoelectric transducer.

As depicted in fig. 3, each of the transducer elements 42 is provided on a separate substrate, preferably formed of steatite ceramic. The upper surface 24 of each of the substrates 20 is a flat surface arranged to provide an angle of incidence α greater than 0 ° and less than 90 ° in the same manner as the upper surface 22 of the substrate 20 in fig. 1. Because the transducer elements 42 are smaller than the transducer 10 of fig. 1, the distributed transducer 10' may have the same effective width as the single element transducer 10 of fig. 1, while enabling a significant reduction in height h compared to the transducer 10 of fig. 1. Thus, higher angles of incidence can be achieved with distributed transducers without resulting in a significant increase in the overall height of the transducer.

In the embodiment of fig. 3, the plurality of transducers 42 form a row of transducers, i.e., a 1 × N array, where N is the number of transducer elements (in this case five). Each of the transducers 42 is oriented in the same direction at the same angle of incidence a. In alternative embodiments, the transducer 42 may be provided with different angles of incidence and may be oriented in different directions. Fig. 4 depicts an embodiment of a distributed transducer 10 "having

transducer elements

42a, 42b oriented in two different directions. In this embodiment, each of the

transducer elements

42a, 42b is constructed to have the same angle of incidence. The transducer 10 "of fig. 4 may be configured as a two-station system, in which elements 42a are grouped together to function as a transmitter and elements 42b are grouped together to form a receiver. In another example (not shown), the transducer elements may be arranged to form a pyramid structure with the four transducer elements oriented at the same angle of incidence in four different directions.

To avoid coupling between different transducer elements 42, an isolation layer 44 may be added to the edge of the substrate 20 to dampen or reflect ultrasonic signals from adjacent transducer elements 42. An example of an isolation layer 44 on the transducer is depicted in fig. 1. Any suitable type of material may be used for the isolation layer 44.

Referring now to fig. 5-10, another embodiment of a system 30 for detecting blood flow velocity and measuring blood pressure is depicted. In the embodiment of fig. 5-10, the system 45 includes a phased transducer array 46 for generating and receiving ultrasound signals for detecting arterial location and measuring blood flow velocity.

The phased transducer array 46 includes an array of piezoelectric transducer elements 48 disposed on a substrate. The transducer array 46 may include any number of elements along the X-axis and Y-axis of the array. For example, the array may comprise a 1 × N transducer array having one element along the X-axis and N (in this case five) elements along the Y-axis (as depicted in fig. 5), or the array may comprise an N × 1 array (as depicted in fig. 6) in which N elements (in this case five) are provided along the X-axis and one element is provided along the Y-axis. A transducer array having a single element in one dimension is also referred to as a transducer row. The array 46 may also include an M N array of transducers, where M is the number of elements along the X-axis of the array and N is the number of elements along the Y-axis of the array, and M and N are greater than 1. In fig. 7, the array is a 5 x 5 array of transducer elements 48.

The parameter p is the pitch between the center of one transducer element 48 and the center of an adjacent transducer element 48. The distance p is advantageously less than half the wavelength of the signal emitted by the array. The wavelength of the signal is given by:

where λ is the wavelength of the signal, v is the ultrasound velocity (v ≈ 3200 m/s for PZT, v ≈ 1560 m/s for human tissue), and f is the frequency of the signal. For the transducer array to operate at a frequency of about 4 MHz, the wavelength is about 0.80 mm. Therefore, in this case, the pitch p should be about 400 μm.

In one embodiment, each transducer element 48 has substantially the same size and shape, with each element being rectangular or square in shape. The transducer elements 48 in the array 46 are simultaneously fed with electrical signals from the phase control system 62, which causes each transducer element 48 to emit an ultrasonic signal or wave.

As is known in the art, the phases of the signals fed to the different elements can be controlled such that the effective radiation pattern (pattern) of the array is emphasized in a desired direction and suppressed in an undesired direction such that the main lobe or beam of the radiation pattern is directed in the desired direction. By adjusting the phase of the signals fed to the elements, the direction of the beam can be changed in a process called beam steering. Thus, a tunable phase shifter (not shown) is associated with each element 48 in the array 46, which enables phase shifting of the electrical signals fed to the transducer elements 48.

As depicted in fig. 8, a phased array 46 having more than one element 48 along the X-axis (i.e., an axis parallel to the longitudinal dimension of the vessel and the direction of blood flow) enables beam steering along the X-axis. This enables the angular component θ of the beam to be adjusted. The angular component θ controls the angle of incidence of the beam with respect to the blood vessel 36. Similarly, a phased array 46 having more than one element 48 along the Y-axis (i.e., the axis perpendicular to the direction of blood vessels and blood flow) enables beam steering along the Y-axis, as depicted in fig. 9. This enables the angular component to be adjustedΦ. With the angular component θ set to the angle of incidence of the transducer 46, scanning the beam along the Y-axis may be used to find the measurement angle at which the blood vessel 36 is locatedΦ _vAs depicted in fig. 10.

The phased array control system 62 is used to control the phase shifts of the transducer elements 48 to produce a beam in a desired direction. The control system 62 includes a processor (not shown), such as a central processing unit, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) device, or a microcontroller. The processor may be configured to execute programmed instructions stored in a memory (not shown). The instructions include instructions for phase shifting and/or for implementing one or more beam steering algorithms.

An embodiment of a transducer element 48 for use in a phased transducer array is depicted in fig. 11. Similar to the transducer of fig. 1, the transducer element 48 includes a piezoelectric substrate 50, an upper electrode 52, and a lower electrode 54. The piezoelectric substrate 50 is formed of any suitable piezoelectric material, including, for example, lead zirconate titanate or aluminum nitride. The upper electrode 52 and the lower electrode 54 are formed of a conductive metal, such as aluminum, an aluminum alloy, platinum, tantalum, or any other suitable conductive metal.

The transducer elements 48 are supported on a carrier substrate 56. The carrier substrate 56 serves as a carrier for the transducer elements 48 and also as a coupling member for coupling the ultrasound signals to the underlying skin and tissue. The base 56 includes a lower surface 58 and an upper surface 60. The lower surface 58 is configured to be placed against a flat surface 26, such as a flat skin area on a patient's body. The upper surface 60 is located on the opposite side of the substrate from the lower surface 58 and is a generally planar surface to which the transducer elements 48 are attached.

To avoid coupling between different transducer elements 48 of the array 46, an isolation layer 64 may be added to the edge of the substrate 56 to dampen or reflect ultrasonic signals from adjacent transducer elements 48. Any suitable type of material may be used for the isolation layer 64.

The upper surface 60 is configured to orient the transducer elements 48 relative to the surface 26 of the skin. For two-dimensional arrays (such as the one depicted in fig. 7), the beam steering can be used to adjust the angular component θ, so a fixed angle of incidence is not necessary for the transducer. Thus, the transducer may be arranged parallel to the surface 26, which results in the transducer lying substantially flat on the substrate.

In one embodiment of the system 45, the angle of incidence of the transducer elements 48 is set to a fixed value that enables the radial component of blood flow velocity to be determined. This may be accomplished by actuating the transducer elements 48 with static, phase-shifted electrical signals that cause the beam to be emitted at the desired angle of incidence. Forming the transducer elements of the array along the Y-axis enables the use of beam steering to locate the measurement angle at which the blood vessel 36 is locatedΦ _v(FIG. 10). In this embodiment, the system may be configured as a two-station system, such as the one depicted in fig. 2, with one phased transducer array configured as a transmitter and one phased transducer array configured as a receiver.

In an alternative embodiment, the phased array 46 may be provided as a row of transducers having a single element width along the X-axis to reduce the number of elements required for the array. In this embodiment, the angle of incidence of each element 48 is fixed to enable the radial component of blood flow velocity to be determined. This may be achieved in the same way as in the embodiment of fig. 1, for example by orienting the upper surface of the substrate at a desired angle of incidence.

The use of a phased array transducer enables the misalignment of the transducer array 46 relative to the blood vessel 36 to be corrected. For example, fig. 12 depicts a phased transducer array 46 that is misaligned relative to the blood vessel 36 by an angle β. To compensate for the misalignment during the determination of the radial blood flow velocity, the angle β must be determined. This can be done using triangulation methods. More specifically, the angle β may be determined using an angle θ, which corresponds to the angle of incidence and an angle Φ, which is related to the measured angle at the location where the blood vessel 36 is located.

Referring to fig. 12 and 13, to determine the misalignment angle β, a first angle θ is provided₁The phased transducer array 46 is actuated and the measurement angle Φ at which the blood vessel 36 is located is identified₁. Then, the beam is steered to a second angle θ₂And identifies the measurement angle phi at which the blood vessel 36 is located₂. Then, it can be determined that the angle is at the first measurement angle Φ₁And a second measurement angle phi₂The distance to the blood vessel 36, which enables the blood flow direction to be identified. Because the central axis of the array 46 is known, the misalignment angle β can be determined so that the misalignment angle β can be compensated for when calculating the radial component of the blood flow velocity.

As an alternative to beam steering with phase shifting, micromechanical mechanisms may be used to adjust the angle of incidence and/or the angle of measurement of the transducer while compensating for misalignment of the transducer relative to the blood vessel. Embodiments of piezoelectric transducers with micromechanical adjusting mechanisms are depicted in fig. 14 to 16. As depicted, the piezoelectric transducer 70 includes a piezoelectric substrate 72, an upper electrode 74, and a lower electrode 76. The upper electrode 74 and the lower electrode 76 are formed of a conductive material, such as polysilicon. The piezoelectric substrate 72 is formed of a suitable piezoelectric material, such as lead zirconate titanate or aluminum nitride.

The transducer 70 includes elements of a phased array 46, such as the phased array depicted in fig. 5-10. The transducer 70 is supported on a carrier substrate 78, which may be formed of silicon, although any suitable material may be used. The transducer 70 is suspended above the substrate 78 by a micromechanical adjustment system 80 that enables the transducer 70 to pivot about a pivot axis P between a first tilted position (fig. 17) and a second tilted position (fig. 18). The micromachined adjustment system 80 includes one or

more spacers

82, 84, the

spacers

82, 84 configured to space the transducer 70 from the substrate 72 to form a gap G between the substrate 78 and the lower electrode 76.

In the embodiment of fig. 14-16, the adjustment system 80 includes a first spacer 82 and a second spacer 84. As depicted in fig. 14, a first spacer 82 is positioned proximate a first corner of the substrate 78 outside of the region on which the transducer 70 is positioned, and a second spacer 84 is positioned proximate a second corner opposite the first corner and outside of the region of the substrate on which the transducer 70 is positioned.

First and

second spacers

82, 84 are connected to transducer 70 by first and

second support arms

86, 88, respectively. A first support arm 86 extends from an upper portion of the first spacer 82 and is connected to the upper electrode 74 of the transducer 70, and a second support arm 88 extends from an upper portion of the second spacer 84 and is connected to the lower electrode 76 of the transducer 70. The first and

second spacers

82, 84 and the first and

second support arms

86, 88 are formed of a conductive material, such as polysilicon, and serve to electrically connect the upper and

lower electrodes

74, 76, respectively, to control and readout circuitry.

The tilting of the transducer 70 to the first and second tilted positions is controlled by setting

electrodes

90, 92 provided on or in an upper portion of the substrate 78. The

set electrodes

90, 92 are formed of a conductive material, such as polysilicon. In the embodiment of fig. 15, the

set electrodes

90, 92 are formed in an insulator layer 94 formed on an upper surface 96 of the substrate 78. Insulator layer 94 is formed of an insulating material, such as silicon dioxide.

The set electrodes comprise a first set electrode 90 and a second set electrode 92. The first set electrode 90 is located on the substrate 78 below a first side portion 98 of the transducer 70 that is positioned on a first side of the pivot axis P. The second set electrode 92 is located on the substrate 78 below a second side portion 100 of the transducer 70, which is positioned on a second side of the pivot axis P. The first and

second set electrodes

90, 92 are separated from each other by an insulator layer 94.

As schematically depicted in fig. 15, the tilt control system 102 is electrically connected to the first setting electrode 90 and the second setting electrode 92. Tilt control system 102 is configured to selectively apply bias voltages to set

electrodes

90, 92 for causing transducer 70 to pivot to first and second tilt positions.

When the tilt control system 102 applies a bias voltage to the first set electrode 92, a potential difference is created between the first set electrode 90 and the lower electrode 76 on the first side portion 98 of the transducer that causes the first side portion 98 of the transducer 70 to be drawn downward toward the substrate 78. As the first side portion 98 moves downward, the transducer 70 pivots toward a first tilted position (FIG. 17), causing the second side portion 100 of the transducer 70 to move upward and further away from the substrate 78.

When the tilt control system 102 applies a bias voltage to the second set electrode 92, a potential difference is created across the second side portion 100 of the transducer 70 between the second set electrode 92 and the lower electrode 76 that causes the second side portion 100 to be drawn downward toward the substrate 78. As the second side portion 100 moves downward, the transducer 70 pivots toward a second angled position (FIG. 18), causing the first side portion 98 of the transducer to move upward and further away from the substrate 78.

When a bias voltage is applied to the first set electrode 90, the transducer 70 pivots until the first side portion 98 contacts the substrate 78 or the insulator layer 94 on the substrate 78. The orientation of transducer 70 when first side portion 98 contacts substrate 78 corresponds to a first tilted position (FIG. 17). When a bias voltage is applied to the second set electrode 90, the transducer 70 pivots until the second side portion 100 contacts the substrate 78 or the insulator layer 94 on the substrate 78. The orientation of transducer 70 when second side portion 100 contacts substrate 78 corresponds to a second tilted position (FIG. 18). In alternative embodiments, other structures may be incorporated onto the base and/or the bottom of the lower electrode to act as stops for limiting the movement of the transducer toward the base and setting the first and second tilted positions.

In the unbiased state, transducer 70 is oriented substantially parallel to an upper surface 96 of substrate 78 (as can be seen in fig. 15 and 16), which results in transducer 70 having an angle of incidence of substantially 0 ° with respect to the blood vessel. When the transducer is in the first tilted position, the transducer 70 is oriented at an angle of incidence α greater than 0 ° and less than 90 ° in the first direction. When transducer 70 is in the second tilted position, transducer 70 is oriented at the same angle of incidence α in the opposite direction. In an alternative embodiment, the angle of incidence of the transducer may be different in the first and second tilted positions. This may be achieved by incorporating an asymmetric stop or limiting structure on the device to limit different degrees of movement of the transducer in different tilt directions.

The micromachined adjustment system 80 may be used to compensate for misalignment of the transducer 70 relative to the blood vessel 30 in a manner similar to that described above with respect to the phased array transducer of fig. 5-10. In this embodiment, transducer 70 is mechanically implemented to angle θ via micromechanical adjustment system 80 by applying bias voltages to

appropriate set electrodes

90, 92₁And theta₂Is moved. Then, beam steering with phase shift is used to target the angle θ₁And theta₂Finding the measurement angle Φ at which the blood vessel is located₁、Φ₂. Then, the angle Φ at the first measurement can be determined₁And a second measurement angle phi₂The distance to the vessel at the time, which enables the blood flow direction to be identified. Since the central axis of the array is known, the misalignment angle β can be determined so that the misalignment can be compensated for when calculating the radial component of the blood flow velocity.

In the embodiments of fig. 14-18, because the angle of incidence is adjusted mechanically, beam steering is not required to redirect the beam, and therefore fewer transducers are required for the transducer array along the X-axis. Thus, in one embodiment, the transducer array has a width along the X-axis corresponding to one transducer element. The number of transducers along the Y-axis may be any suitable number that provides the desired angular resolution and aperture size for finding the measurement angle at the location where the blood vessel is located.

The micromechanical adjustment system 80 of the embodiment of fig. 14-18 is configured such that only one angle of the transducer can be mechanically adjusted. In an alternative embodiment, the mechanical adjustment system may be configured such that only the measurement angle of the transducer is mechanically adjustable, while enabling adjustment of the angle of incidence by beam steering with phase shifting.

In another alternative embodiment, the micromechanical adjustment system may be configured such that both the angle of incidence and the angle of measurement of the transducer can be adjusted mechanically. The transducer array includes an array of piezoelectric transducer elements, such as the piezoelectric transducer elements depicted in fig. 5-7. The array may comprise a 1 × N array, an N × 1 array, or an M × N array.

In this embodiment, the adjustment system and transducer may be configured similar to a biaxial micromirror, such that the transducer can tilt about two perpendicular axes. This embodiment completely eliminates the need for phase shifters, as no beam steering is required to adjust the angle of the transducer.

Another embodiment of a system 108 for detecting blood flow velocity and measuring blood pressure is depicted in fig. 19. In this embodiment, the piezoelectric transducer arrangement of the system is configured to implement both a multiple-input multiple-output (MIMO) ultrasound transducer array and a phased transducer array. The system includes at least one ultrasound transducer array 110, a phased array control system 112, and a MIMO array control system 114.

The transducer array 110 may include any number of elements along the X-axis and Y-axis of the array. For example, the array may comprise a 1 × N array, an N × 1 array, or an M × N array, such as the arrays depicted in fig. 5-7, respectively. The elements in the array may also be shifted, staggered, or offset from each other in either direction.

The system 108 may comprise a single station system in which the transducer array 110 is used to both transmit and receive ultrasound signals. Alternatively, the system may comprise a two-station system as depicted in fig. 20. In a two station system, the first ultrasound transducer array 110a serves as the transmitter of the system and the second ultrasound transducer array 110b serves as the receiver of the system.

The transducers for transmission are operably coupled to receive electrical signals from phased array control system 112a and MIMO array control system 114 a. The receiving transducers output electrical signals to phased array control system 112b and MIMO array control system 114 b. The phased array control system 112b and the MIMO array control system 114b are configured to process the electrical signals to determine information about the blood vessel using various techniques and algorithms known in the art.

The piezoelectric transducer elements of the array may have the same configuration as any of the transducer elements of the embodiments discussed above. Using the transducer elements of fig. 11 as an example, each transducer element of the array includes a piezoelectric substrate 50, an upper electrode 52, and a lower electrode 54. The upper electrode 52 and the lower electrode 54 are formed of a conductive material, such as polysilicon. The piezoelectric substrate 50 is formed of a suitable piezoelectric material, such as lead zirconate titanate or aluminum nitride. In one embodiment, each transducer element has substantially the same size and shape, with each element being rectangular or square in shape.

To avoid grating lobes when the transducer array operates as a phased array, the pitch between the centers of adjacent elements in the array is advantageously less than half the wavelength of the signal emitted by the array. As mentioned above, to operate the transducer array at a frequency of about 4 MHz, the wavelength is about 0.80 mm. Therefore, the pitch should be about 400 μm.

The phased array control system 112a is configured to supply the same electrical signal or waveform to the transmit transducers, steering the ultrasound beam in the desired direction with a phase shift and amplitude setting. Using multiple transducers to transmit and receive the same signal results in significant transducer gain and good signal quality.

MIMO array control system 114a is configured to supply each of the transmitting transducers with an arbitrary waveform. To this end, MIMO array control system 114a includes a waveform generator (not shown) for each of the transducers. The waveform generator is configured to generate a different waveform for each of the transducers. These waveforms may be either related to each other or unrelated to each other and may be separated in the time, spectral and/or spatial domains. It is also important that these waveforms do not interfere with each other. One way to achieve this is to use Time Division Multiplexing (TDM) switched MIMO.

Each receiving transducer receives a reflected signal from each of the transmitting transducers. Due to the difference in waveforms, the reflected signals may be associated with the transmitting transducer that transmitted them. The transmit array of N transducers and the receive array of K transducers result in a K x N virtual array from K + N elements. This enables a MIMO array to have a large virtual aperture and a higher resolution angle than a corresponding phased array.

The phased array control system and the MIMO array control system may each include a processor (not shown), such as a central processing unit, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) device, or a microcontroller. The processor may be configured to execute programmed instructions stored in a memory (not shown). The instructions include instructions for phase shifting and/or for implementing one or more beam steering algorithms.

The blood flow velocity detection system 108 includes switching

devices

116a, 116b configured to switch between the phased

array control systems

112a, 112b and the MIMO array control systems 114a, 114b to the input of the transmit array 110a and the output of the receive array 110b, respectively, so that these transducer arrays can operate as both phased and MIMO transducer arrays as desired. Any suitable switching configuration and/or method may be used for the

switching devices

116a, 116 b.

In operation, inputs to the transducer array are first switched to the MIMO array control system 114 so that the transducer array 110 operates as a MIMO transducer array. The MIMO array control system 114 supplies the transmitting transducer 110a with an arbitrarily different waveform, which causes the transducer to transmit an ultrasound signal directed generally in the direction of the blood vessel. The reflected signal is received by the receiving transducer 110 b. The MIMO array control system 114 evaluates the output of the receiving transducer to locate the blood vessel.

The inputs to the

transducer arrays

110a, 110b are then switched to the phased

array control system

112a, 112b so that the transducer arrays operate as phased transducer arrays to take advantage of the high transducer gain and better signal quality of the phased transducer arrays, and because the incoming and outgoing beams can be steered by beam steering with phase shifting.

One purpose of the combined MIMO array and phased array blood flow velocity detection system is to avoid the use of high resolution algorithms, such as the multiple signal classification (MUSIC) algorithm. To accomplish this, the transducer may be actuated as a sparse (sparse) transducer array. By omitting some of the transducer elements from being actuated to generate an ultrasound signal, the transducer array may operate as a sparse array. In one embodiment, the transducers may be omitted from being actuated in a random pattern as part of a MIMO transducer array, such that different pitches or spacings are provided between elements in the array. The sparse spacing allows for an even larger virtual aperture size, which in turn leads to higher angular resolution. This gives the opportunity to achieve better spatial/angular resolution and better angular estimation, so that the vessel is located with greater accuracy.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications, and further applications that come within the spirit of the disclosure are desired to be protected.

Claims

1. A system for detecting blood flow velocity within a blood vessel, the system comprising:

a transducer array comprising a plurality of ultrasonic piezoelectric transducers, each of the transducers comprising:

a carrier substrate having an upper surface;

at least one spacer extending upwardly from the upper surface;

a transducer element attached to an upper portion of the at least one spacer such that the piezoelectric transducer is spaced apart from the upper surface of the substrate, the piezoelectric transducer comprising an upper electrode and a lower electrode;

a set electrode positioned on an upper surface of the substrate below the piezoelectric transducer; and

a tilt control system configured to apply a bias voltage to the set electrode, the bias voltage configured to create a potential difference between the set electrode and the lower electrode that causes the transducer element to pivot about a pivot axis between a first tilt position and a second tilt position,

wherein the transducer array has an X-axis and a Y-axis, the transducer array configured to be placed on a skin region, the X-axis substantially aligned with a blood vessel below the skin region,

wherein the transducer elements define a first angle relative to the blood vessel in the first tilted position and a second angle relative to the blood vessel in the second tilted position.

2. The system of claim 1, wherein the set electrode comprises a first set electrode positioned below a first side portion of the transducer element, the first side portion being located on a first side of the pivot axis, and a second set electrode positioned below a second side portion of the transducer element, the second side portion being located on a second side of the pivot axis.

3. The system of claim 2, wherein in the first tilted position the transducer elements define a first angle of incidence relative to the blood vessel, and in the second tilted position the transducer defines a second angle of incidence relative to the blood vessel.

4. The system of claim 3, further comprising:

a phased control system configured to cause the transducer array to emit an ultrasound beam, the phased control system configured to steer the beam along the Y-axis to locate a measurement angle for the array transducer at a location where the blood vessel is located.

5. The system of claim 1, wherein the upper and lower electrodes are formed of polysilicon.

6. The system of claim 2, wherein the carrier substrate comprises an insulating layer on an upper surface of the substrate, and

wherein the set electrode is formed in the insulating layer.

7. The system of claim 6, wherein the carrier substrate is formed of silicon.

8. The system of claim 6, wherein the lower electrode is positioned in contact with the insulating layer when the transducer element is in the first and second tilted positions.

9. A method of compensating for misalignment of a phased transducer array relative to a blood vessel, the method comprising:

placing a transducer array on a skin region, the transducer array comprising a plurality of transducers, each of the transducers comprising:

a carrier substrate having an upper surface;

at least one spacer extending upwardly from the upper surface;

a transducer element attached to an upper portion of the at least one spacer such that the transducer is spaced apart from the upper surface of the substrate, the transducer comprising an upper electrode and a lower electrode, the transducer element being pivotable about a pivot axis between a first tilted position and a second tilted position; and

a set electrode positioned on an upper surface of the substrate below the transducer;

positioning a first measurement angle at a location at which the blood vessel is located by steering an ultrasound beam emitted by the transducer array with a phase control system, wherein the respective transducer element is in the first tilted position;

applying a bias voltage to a set electrode of the respective transducer to create a potential difference between a transducer element of the respective transducer and a lower electrode of the respective transducer, the potential difference causing the respective transducer element to pivot from the first tilt position to the second tilt position;

locating a second measurement angle at a location at which the blood vessel is located by steering an ultrasound beam emitted by the phased transducer array with the phase control system; and

determining a misalignment angle of the transducer based on the first measured angle and the second measured angle.

10. The method of claim 9, wherein the first tilt position defines a first angle of incidence for the transducer element, and

wherein the second tilt position defines a second angle of incidence for the transducer element.

11. The method of claim 9, wherein the set electrode comprises a first set electrode positioned below a first side portion of the transducer element, the first side portion being located on a first side of the pivot axis, and a second set electrode positioned below a second side portion of the transducer element, the second side portion being located on a second side of the pivot axis.

12. The method of claim 9, wherein the upper and lower electrodes are formed of polysilicon.

13. The method of claim 12, wherein the carrier substrate is formed of silicon.

14. The method of claim 13, wherein the carrier substrate comprises an insulating layer on an upper surface of the substrate, and

wherein the set electrode is formed in the insulating layer.

15. The method of claim 14, wherein the lower electrode is positioned in contact with the insulating layer when the transducer element is in the first and second tilted positions.